Is it really worth the extra work to build a 383?

[jim_in_dorris]

Not sure if I titled this correctly, I am looking at both a 350 +.030 rotating assembly and a 383 rotating assembly with identical parts other than the stroke on the crank. Scat 9000 crank, H-beam rods, probe forged -12.5 cc dished pistons, new harmonic balancer, new heavy duty flex plate, rings and bearings completely balanced. I think I will use a Dart shp head, regardless. When I run the numbers on Comp-cams software (8-407-8 .. 252/258 .472/.480) I get .5 hp loss and 30 #/ft of torque gain for the 383 over the 350. When I run DD I get the same HP loss, but only about 25 #/ft of torque gain. I know that I am horsepower limited by my cam choice, but I want low end torque, the engine will rarely see rpm's north of 3500. What I did discover using my DCR calculator is that with a .045 quench setting, and 64cc combustion chamber I go from 9.4:1 SCR to 10.1:1 SCR. That's way more than I want. I can lower the CR by going with the 72cc combustion chamber version of the Dart shp heads, which puts my SCR back to 9.4:1. Is there a noticeable performance difference between the two sizes of combustion chamber if I maintain the same SCR? I thought that maybe I could use a bigger intake runner so I ran the numbers with 180 and 200 CC intakes, and it moves my curves up the RPM range, but doesn't seem to affect the total power any. Given that I am after dead reliable over power, does it make sense to even go to the 383? I know that this discussion has been beat up, but mostly for guys that want all out power. If I was after that, I would use a different cam, bigger heads, and go 383, but that's not what I want. Also, would I give up mpg with the 383 over the 350? I am building this motor for my alaska trip next summer, and will be towing a 22-24 foot travel trailer. I know I won't get great mileage with that much weight behind me, but after the trip, I will drive this truck daily.

[1project2many]

IMO, not usually.

I've built modern 383's for guys and while they make plenty of power and torque, they're just not my style. There's only one real reason why the 383 exists and that's because "back in the day" a guy could put the biggest factory crank into a 4" bore block and try to sneak it past the other racers as a 350. Like the 302, legend grew and the 383 gained popularity. With custom cranks you can build almost anything you want. I dynoed a 396 smallblock for a guy that made so much torque the friction brakes on our Dynojet would only hold the drums to about 20% throttle. The Impala SS that it was installed in was stupid quick for a large car and he smoked a couple of race built THM400s just playing around on the street. Yet it wasn't obnoxious at idle or low speed.

Large stroke engines like large flow heads. The old 383 stroker race engine would run out of power 1k rpm below the 350 with the same heads. It made torque so we'd gear the rear differently. Smart guys always figured something was up when we were keeping up with the pack (or leading it) but our engine wasn't screaming like theirs. But the point is the heads couldn't flow enough air for the 383 to be effective at the same rpm. Yes, we got the same job done or slightly better but I always looked at the opposite side... a lot of work and a lot more displacement but it didn't seem like a huge gain. If the Dart heads aren't great for flow, I'd stay with the smaller displacement engine or choose another head.

If the ring pack is closer to the top of the piston there's going to be some advantage for emissions and power, but it's slight. The increased rod angularity and resulting friction at the cylinder wall can easily offset it. You lose rod to stroke ratio as well and I feel that greater R:S engines tend to run smoother and get better mileage.

Try to keep quench small. .030" - .032" is the target. Reducing quench like this helps keep detonation at bay. Apply ceramic thermal barrier coating to the piston tops and the combustion chambers and you can run 10:1 with no worries. With those aluminum heads you're looking at, 10:1 is probably a non-issue anyway but I think you're going to play it safe at 9.5:1 or lower.

A trip to Alaska... sounds like it could be quite an adventure.

[gregs78cam]

I am running similar setup in the camaro but with 6" rods. I had my block decked to 0.000" to tighten up the quench. With aluminum heads I am running 10.5:1, but I have never tried to run 87 octane in it. Cam is a bit smaller than mine so a little less compression won't hurt. If you are building the engine anyways and there is room in the budget, I see no reason not to go 383. You basically give up very little and gain usable torque.

[jim_in_dorris]

1project2many, I chose the heads because of budget constraints, and the fact that they have EGR crossovers. I don't really want a race engine, like I said. The dart heads are a medium flow head, nothing like AFR or TrickFlow, but I should be able to sneak them past the smog nazis. What head gaskets should I look for to reduce my quench space. I am having the block decked at .005 in the hole, and most head gaskets are about .040 that I looked at. I don't really have the budget for ceramic coatings, and really want to keep the CR down so I can run mid-range gas. In a go-fast project, I probably would be doing the opposite, and spending the money. The Alaska trip is to visit the daughter, hopefully she will be moving to Anchorage from Juneau this spring so we can drive to see her. Of course, the sights and fishing that go with it are just icing on the cake. Over 2700 miles each way.

Greg, like I said, if this was going in something like your 78 camaro, it would be a totally different build, and I probably would go 383 or bigger without thinking about it. I kind of like the thought of a 406 or bigger small block. Does the Dual TBI feed the beast? Sounds like a lot of fun.

[EagleMark]

For a rig like that and the aventure planned I would run a very stock TBI motor, maybe an L31 Vortec to TBI? Cause I just tuned one in a 1990 Chevy TBI truck. Reliable, cheap, easy to repair on road if need be. Depending on tire size gear it! My Suburban is stock other then ECM. Has 235/75r-15 tires and 3:73 gears with towing package. Loaded, 40 gallons of gas, 40 gallons of water and a 22 foot travel trailer full! It pulls the mountain passes here fine and still gets 10 plus MPG. I only used OD on flatlands to 60 MPH, pulls most passes at 45-50.

No lean cruise for towing!

[1project2many]

1project2many, I chose the heads because of budget constraints, and the fact that they have EGR crossovers.

But why aluminum? And if I read correctly, those heads don't use a fast burn chamber??

What head gaskets should I look for to reduce my quench space.

You're much more limited if using an aluminum head. With iron you could use an old Chevy stamped steel gasket.

I don't really have the budget for ceramic coatings

I just bought a bottle of heat barrier and a bottle of dry film lube. Together they cost $62 with shipping. A cheapie harbor freight airbrush like I started with is maybe $30

and really want to keep the CR down so I can run mid-range gas.

Done correctly, with or without coatings, you'll be able to run low range gas.

I have friends living in Homer, AK but I've never gotten to see them. I think the trip is nearly double the mileage for me, though.

[gregs78cam]

Greg, like I said, if this was going in something like your 78 camaro, it would be a totally different build, and I probably would go 383 or bigger without thinking about it. I kind of like the thought of a 406 or bigger small block. Does the Dual TBI feed the beast? Sounds like a lot of fun.

You can build a torque monster 383 and not HAVE to wind it up. An aluminum head only GIVES you the ability to run a higher compression, doesn't mean you have to. With 180cc runners and the size of cam you are talking I think it would be great combo. I went just a little wilder than your specs because obviously it was going in the camaro, but even mine makes more torque than hp. And yes two TBI's are more than adequate. That cam should be no problem to tune either way.

[jim_in_dorris]

Well, the marine stuff is out, not only after 1project2many's comments, but my research. The 302 idea would work if I saw high rpm's, however using my handy dandy self made excel spreadsheet, with my 3.73 gears, 700R4 and 265/70/15 tires, at 2350 rpm in 3rd gear I am doing 55.5 mph, 80 in overdrive (not that I would tow in OD). if it kicks down to second, 3500 rpm is 51 mph. I need torque in that kind of range. The 406 was a torque monster on DD, but I give up a lot when I switch back to a standard flat tappet cam. The trailer loaded is going to be somewhere just under 5000 lbs. loaded, so I will need lots of torque. I guess my real question is with the 350, I get about 415 #/ft of torque from 2000 to 4000 rpm. Will that work? The 383 gives me 450 #/ft of torque from 2000 to 3500 rpm. obviously this is DD, so results may vary. My question is mainly if I have over 400 #ft of torque at the flywheel, will it do the job towing? BTW, thanks everybody for chiming in, I really appreciate talking to people that aren't trying to sell me something but have real world experience with the kind of motor I am interested in building.